Fix lots of bugs

1. Group: if a user is not in some private group anymore, geting group
   data by Fb::api() returns an error. If the user is not in the group
   indeed, remove the group id from the user's 'groups' field. If the
   removed group is the only group, set status to 'stopped'
2. Move Texts::replaceTab() to Util::replaceTab()
3. Mark errors from RSS reader as 'RSS Reader'. See
   plugins/rss_reader.php
4. Alternate: use direct if instead of typeof xxx != 'undefined'
5. Alternate and Post: remove the field 'processed' in error handing
6. Alternate: Fix: set user status when updating user list
7. Post: modify some error reporting formats, especially add backtrace
Merge 2 FB api calls into one - name/uid and groups

and modify some error handling codes
Alternate: use one timer instead of lots of timers

Other changes:
1. Add Pause in alternate.php, though seems buggy
2. Fix a bug in plugins/rssReader.php